1. Field of the Invention
This invention relates to a liquid injection recording method, and more particularly to an on-demand type liquid injection recording method which is capable of accomplishing harmonious expression on a recording medium by the control of a voltage pulse applied to electro-mechanical converting means.
2. Related Background Art
A liquid injection recording apparatus such as an ink jet printer is instructed such that ink is supplied to a recording head and the ink in the recording head is are propelled favored a recording medium to accomplish recording.
As energy converting means for discharging the ink, there is known electro-mechanical converting means such as a piezo-electric element or electro-thermal converting means such as a heat generating resistance member in an ink discharge system utilizing heat energy.
The present invention is directed, above all, to a liquid injection recording method and apparatus using said electro-mechanical converting means.
In the liquid injection recording method of this type, there is adopted a method of disposing electro-mechanical converting means, for example, a piezo-electric element, in the circumferential wall portion of the pressure chamber, for example, of a liquid injection recording head (ink jet head), applying a voltage pulse in the direction of polarization to the piezo-electric element and abruptly reducing the volume of the pressure chamber, thereby causing liquid droplets for recording to be discharged.
FIG. 3 of the accompanying drawings shows a longitudinal cross-section of the essential portion of a recording head used in the liquid injection recording method of this type, and FIG. 4 of the accompanying drawings shows an enlarged longitudinal cross-section of the electro-mechanical converting means in FIG. 3.
In FIGS. 3 and 4, a plurality of tubular liquid flow paths 2 are connected in a sub-tank 1 and a cylindrical piezo-electric vibrator 3 is provided on the outer periphery of each liquid flow path and the end of each liquid flow path is tapered to form an ink discharge port 4, whereby the dot forming portion of the recording head is constructed.
The sub-tank 1 is connected to a main tank, not shown, through an ink supply tube 5 and connected to a suction pump and a waste liquid tank, not shown, through a suction tube 6, and is designed to maintain the level of the ink 7 therein within a predetermined range.
Said cylindrical piezo-electric element 3 is secured to the peripheral surface of said liquid flow path 2 by means of an adhesive agent 8. The liquid flow path is made of a relatively hard material such as glass or a metal to propagate the vibration of the piezo-electric vibrator 3 through the liquid (ink) in the liquid flow path 2, and constitutes a nozzle at the end thereof to form a discharge port for discharging recording dots (liquid droplets).
A filter 9 is mounted at the entrance of the liquid flow path 2 which is adjacent to the sub-tank 1 so that by providing a predetermined flow resistance, proper balance is maintained between the pressure in the direction of discharge during the discharge of liquid droplets and in the opposite direction, to thereby adjust the discharge state of liquid.
During recording, when a voltage pulse is applied to the cylindrical piezo-electric vibrator 3 to cause vibration thereof, the vibration is propagated to the liquid flow path 2, whereby the pressure of the liquid (ink) in the liquid flow path 2 is changed to permit liquid droplets to be discharged from the discharge port 4 and thus, dot recording is accomplished.
In the liquid injection recording method of this type, by varying the magnitude of the voltage of the voltage pulse applied to the piezo-electric vibrator 3 for the formation of liquid droplets, the diameter of dots on a recording medium (paper or the like) can be controlled to accomplish harmonious expression.
In this case, the greater the voltage value of the voltage pulse, the greater the dot diameter and the wider the harmony range that can be obtained.
Now, the formation of liquid droplets is subject to influence by environmental conditions, particularly, temperature. That is, when the liquid injection recording apparatus is placed under a high temperature, the viscosity of liquid becomes lower than under the normal room temperature environment and thus, the liquid droplet formation conditions change.
However, in the conventional liquid injection recording method, if the voltage value is increased to increase the dot diameter with the viscosity of liquid being reduced under a high temperature, the vibration of the meniscus surface during the discharge of liquid droplets become sufficiently vehement to cause bubbles to be produced in the liquid flow path 2 and thereby cause unstability of discharge, or cause the discharge of the phenomenon that small-diametered liquid droplets of low discharge speed after the discharge of original liquid droplets, thereby degrading the quality of recording, and this has led to the problem that the range of variation in the voltage of the voltage pulse is limited by the state of discharge in a high temperature environment and the harmony range cannot be sufficiently widened.